The invention concerns a component working with surface-proximal acoustic waves, in particular a filter with a network structure, in which component resonators are embedded.
Today, SAW, or surface acoustical wave, filters are predominantly used as bandpass filters in the RF range in the front end of end apparatuses of mobile communication, for example in mobile telephones. These are significantly fashioned as reactance or DMS filters.
Circuits of DMS filters with reactance elements are also known, in particular with one-port resonators executed in SAW technology. Thus, for example, a DMS filter is known from DE 198 18 038 A in which two DMS filters circuited in serial or in parallel are circuited in series with reactance elements on the input or output side. Moreover, it is proposed there to arrange both DMS filters inside an acoustic track and two adjacent DMS filters are to be divided via intermediate reflectors.
Further known filters are also two-port resonators that, however, can only seldom be used in the RF range due to their narrowband transmission characteristics.
Depending on the desired characteristic profile, one of the technologies can be preferable. For example, with closely adjacent frequency bands for selection, higher demands are made on the skirt steepness of those passband edges that are close to the respectively adjacent frequency band. Different skirts can favor different technologies. Reactance filters are additionally characterized by higher power stability. A desired demanding characteristic profile for an RF filter, in particular for a new transmission technology, can often no longer be realized with known, “pure” technologies. Thus, for example with reactance filters, an unwanted “ripple” occurs in the transmission range that is based on the finite length of the series resonator. Likewise, the insertion attenuation is increased based on the finite length of the resonators used in reactance filters.
From U.S. Pat. No. 5,486,800 C1 it is known to serially arrange a plurality of identical interdigital transducers directly adjacent to one another within only one acoustic track such that an acoustic coupling of the interdigital transducers ensues. The interdigital transducers are electrically connected in series, whereby a parallel branch connected to ground respectively branches off between two interdigital transducers. In the type of ladder-type structure, a further parallel interdigital transducer is arranged in every parallel branch. A plurality of parallel interdigital transducers can also be arranged within an acoustic track and likewise be acoustically coupled. Each track with acoustically coupled interdigital transducers can be bordered on both sides by one acoustic reflector.